Railway train communication and alarm system using modulated carrier currents



P. N. BOSSART RAILWAY TRAIN COMMUNICATION AND A Oct. 11, 1949;

LARM SYSTEM USING MODULAI'ED CARRIER CURRENTS 3 Sheets-Sheet .1

Filed Jan. 30, 1945 mg 5 Q Q My I Q NN INVENTQR Paul M flossar'. BY aimH117 A'ITORNEY P. N. BOSSART I 2,484,680 RAILWAY TRAIN COMMUNICATION ANDALARM SYSTEM USING MODULATED CARRIER CURRENTS 3 Sheets-Sheet 2 I N kwwmmmw R A% Oct. 11, 1949.

Filed Jan. 50, 1945 Oct. 11, 1949. P. N. BOSSART RAILWAY TRAINCOMMUNICAT ION AND ALARM SYSTEM USING MODULATED CARRIER CURRENTS v 3Shee ts-Sheet 3 Filed Jan. 30, 1945 NB gwmmmmw Q NQ U INVEN'TOR.

Paa! M flassap.

AS SN U HIS ATTORNEY Patented Oct. 11, 1 94 9 -RAI'LWAY TRAINCOMMUNICATION ALARM SYSTEM Union Switch & Signal Company,

AND

, USING MODULATED panama :CUR It ENTS Paul N. Bssart, Cheswick, Pa.,assignor to The Pa., a corporation, of Pennsylvania Application January.30, 1945, Serial '19 c ai s. (01. 179-82) My invention relates torailway train communication systems, and more particularly to multiplechannel train communication systems.

When train communication is installed on, all or nearly all of thetrainsof a railway division and also at one or more gwayside stations, someform of selection is necessary. That-is to say, ;if end to endcommunication is being carried on by the crew of one train the traincrewof asecond nearby train should be able to carry on come municationwithout interference between the two trains. Also an operator at aWayside ,station should be able to communicate with a train withoutinterfering'with end to end" communication of other trains.Furthermoraif the ofiic'eopera-. tor or any other station should wish tobreak in on a conversation to issue train orders,.such should bepermitted. In other words, when an entire railway division is equippedfor train communication, a, plurality of different communicationchannels and a break in feature are essential.

Accordingly, a feature of my-inventi'on is the provision of novel andimproved apparatus for a multiple frequency channel train communicationsystem.

Another feature of my invention is the provision of railway traincommunication apparatus incorporating novel means for selecting aparticular frequency channel of a plurality of different channels forcommunication. I

Still another feature of my invention is-the provision of railway traincommunication apparatus incorporating novel means for calling a train orstation on each one of a plurality of dif ferent frequency channels. j

Again, a feature of my invention is theprovie sion of apparatus of thetype here contemplated for calling a station that is already incommunica-e tion and for cyclically calling a station on'each ofaplurality of different channels. r

A further feature of -my invention isthe "provision in apparatus of thetype here involved. of novel means to reduce the receiver sensitivityfor the channel in use during a; conversation sothat the integrity ofthe transmitter and receiver may be checked by side tones from-thereceiver." 1

Another feature of my invention is the'provi-J sion of traincommunication apparatus incorpo rating novel means t'o'suppressbackground noises and to 'pIOVide We...

Swissvale,

No. 575,311 I '2 Again, a feature of my invention is the provision ofimproved railway train communication apparatus using frequencymodulation with a trackway transmitting circuit which includes thetrackrails and line wires and other conductors extending parallelalong'the railway.

Other features, objects and advantages of my invention will appear asthe specification progresses.

I attain the aforementioned features, objects and advantages of myinvention by the provi-' sion of transmitting apparatus capable of beingconditioned to supply frequency modulated carrier telephone current ofany one of a plurality of difierent carrier frequencies, and receivingapparatus responsive to each of said frequency modulated carriertelephone currents. That is, each such carrier serves as a frequencychannel. The receiving apparatus is-normally conditioned to receive acalling current on any one of the channels, but thetransmittingapparatusis excited and made active only during periods current is to be sentout; Preferably the receiving apparatus includes an individual orindependentreceiver for each channel, the different'receivers beingconnected in multiple to a loud speaker. to sound a calling tone signalreceived on any one of the channels, each channel having its individualtone. Through the hook switchoi a telephone hand set and other manuallyoperable switches, the hand set when removed from the hook switch isconnected to the channel of which a calling signalhas been received, butthe loud-speaker is left connected to the other channels to sound acalling signal if it is found'necessary'to break in onthe conversationbeing carried on through the selected channel. That is, when the handset is hung on its hook switch, a calling signal or speech on any one ofthe frequency channels is received in the loud-speaker, but when, thehand set is off the hook the channel selected for conversation isconnected to the hand set only and the other channels are connected tothe loud-speaker.

,In addition, each receiver includes-ineansto check the operativeness ofthe transmitter and of the receiver of the channel in use. To this endthe receiver of the channel in use is kept active during transmissionbut itssensitivity is greatly reduced because of the very strong energyit will pick" upifrom'the local transmitter. This reduction insensitivity is made only during the talking period. Thus there issounded in the local earphone at a normal energy level the conversationthat is being sent out. Reduction in the sensitivity of the receiverduring the transmitting period prevents overloading of the receiver andpermits self-monitoring at a comparatively low energy level.

The transmitting apparatus is preferably of the reactance-variation typeof frequency modulating transmitter, and: its various elements are,-provided with different capacitors through which the transmittingapparatus can be selectively condir. tioned for any one of a pluralityof different frequency channels.

On railway trains there exists ,a large amounts of background noisewhich if transmitted may be objectionable, and to overcome this Iprovide, an

adjustable microphone circuit'network whose;

sensitivity can be set so that the usual background noise is ineffectiveto operate the transmitter. This requires the speaker to speak 'rela-'tively loud and close to the microphone. In connection with suchsensitivity adjustment of the microphone I provide the transmittingapparatus with indication means sothatthe speaker can readily tell whenhe is-talking loud enough'to cause the proper frequency swing of thetransmitting apparatus. Such indication means preferably includes a gasdischarge type of lamp connected to the-microphone circuit through anamplifier to flash'the lamp when the speaker is speakin at the-correctloudness.

Pro-emphasis is of a considerable help inimproving the signal noiseoperate at times near the noise level, and pro-- emphasis-is provided inthe apparatus by -a resistance-capacity circuit in the microphonenetwork; In adjusting the microphone network,--it isimportant that theamount of pro-emphasis does not change and a resistance pad is used-toaccomplish such results.

I provide a calling current by impressing an audio frequency on themodulator through contactsrof. a calling relay, a different pitch-beingused for each channel. Such calling frequency is attained through theuse of an adjustable-elem; tron tube oscillator and preferably I switchan amplifier: tube of the indication means to an os-- cillator to. serveas a tone generator. Also--the secondary winding of themicrophonetransformer ispreferably switched -to serve-asthe induc tanceof the oscillating circuit'of thetone gen orator- Separateoscillatortubeand inductance can be used, if desired.

I provide a special control unit together with control relays to governthe condition of;--the transmittin apparatus for-operation-at the dif--ferent channel frequencies and to efiect the differentcallingconditions. This control means also includes an emergency calling measwhich when set into operation functions to send call-1 ing pulsescyclically on each of the frequency channels.

Atwayside stations I preferably couple the apparatus to thetrackwaytransmitting circuit by connection to a line wire extendingalong the railway. Switching means is used to increase the voltageapplied to the line wire at the lowercarrier frequency.

I shall describe one form of apparatus embody ing my invention, andshall then point out,the novel features thereof in claims.

In the accompanying drawingsLFigs. 1 and .2

with Fig. l placed above Fig. 2 are diagrammatic ratio in systems which\on .v hicles .of

views showing one form of apparatus embodying my invention when usedwith a train carried station of a two frequency channel traincommunication system. Fig. 1 discloses the transmitting apparatus,certain control relays, and a source of power, and Fig. 2 discloses thereceiving apparatus and a control unit. Figs. 3 and 4 are diagrammaticviews showing wayside station line wire connections for the apparatus ofFigs. 1 and 2.

In each of the several views like reference characters are'used todesignate similar parts.

Referring to Figs. 1 and 2, the reference character CO designates avehicle of a railway train ,on, which theicomm-unication apparatus ismounted; This vehicle. CO may be the caboose of a freight train; for;which two way communication with remote stations is provided, suchremote stations being on another vehicle of the same train,

other trains and at wayside stations. Eachsuch remote station will ofcourse be provided with. communication apparatus simi- 'lar tothatdisclosed in Figs. 1 and 2.

The caboose CO is provided with a source of power, such as the usual 32volt car lightin system theterminals of this source being designated B32and AN32L' The -32 volts of this source are converted into avoltage-suitable for use with electron tubesthrough-a motor generatorMG, a motor lll :of whichis-connected-to the 32 volt source and agenerator I of which is provided with terminals B lflflt'and. N400 fromwhich a relatively: high voltage is obtained. The positive terminalB32t'and the. negative terminal N Q93 are connected to: agroundelectrode I 2." The caboose. is alsoiprovided with a series ofcontrol-relays. l9, 25.,.'50:-"and.16,= and..a control .unit indicatedaswa whole byta dashiand dot rectangle CU; which relays andunit will bereferred to from time. to time .as. the specification progresses.

A dashand dot rectangle v TA -.(Fig. 1) designates -theatransmittingapparatus. This trans mitting. apparatus vTA comprises as essential.ele'-.

ments a :microphonecircuit network including a transformer'Tl and a.potential divider Mt, a reactancemodulating tube. VI; san oscillator:tube V2, a driver amplifier tube V3,:a power-amplification stageincluding tubes ya and, V5, indication mplifier tubes VBand-VLand ;acalling means which includes tube V6 as an oscillator. and a windingof.thetransformer T! as .5 the inductance of the associated: oscillatingcircuit; 1'

A primary-winding l 4 of transformer ,I i is connected (to themiorophonecircuit in a manner'to appear hereinafter, and secondary winding i5 oithe transformer is included 1 1113, controlgrid circuit for the,reactancatube l. This grid circuit extends; from control id wil throughchoke coil, 23 and either ofytwo alternativemaths, to cathode I8 of thetube The first path includes back contact l4 3 -.of-;rel-ay 56 -tobereferred to later,- adjustable terminal .-I 44. of potential dividerI4fl,,.wire Jl, winding 15-, back contact it of relay |9v also tobereferred, to later,-ground electrodes 20 and 2| and, biasing unit =22, a The, second path includes frontcontact, I42 ofrelay, 50, wire 1|andthen-ce thesameasthexfirst path. The plate. circuit for tube-Viis-provided with power from terminalB400Hof theigenerator 1 I, throughfront contact 24, .of. a directional relay. 25 governed in amannendescribed later..wire 26,.resistors 21,an d .28; 'mpedance,29,.plate, 30, and tube space v The oscillator tube V2 hasassociatedithere with an oscillating circuit comprising. inductance 33and capacitor 34. Aphase shifting networkv comprising capacitor '35 andresistance 36 in series is connected across theoscillating circuit andassures the correct phasing of the reactance mod ulator tube Vl. Cathode31 .of tube-V2 is connected to an intermediate terminal of winding 33 ofthe oscillating circuitQandplate 38 ofthe tube V 2 is provided withpower from terminal B400 of the current source through a circuitincluding front contact 24 of relay 25, wire 26, andresistors 21 and 9.The parts are so proportioned that oscillations of a preselected carrierfrequency which I shall call frequency I are produced, an adjustment ofthe inductance of the coil 33 for such frequency being provided throughanfiadjustable core structure asindicated in Fig. 1.

The control grid circuit and-plate circuit of tube VI are coupledthrough capacitors 3i and 32 to the oscillating circuit with the .resulttube Vl serves as a variable reactance for the oscillating circuit. Thusvoltages applied to the control grid of tube Vl cause variations in thereactance of the tube as it appears to the oscillating circuit and inturn cause corresponding frequency variations of the oscillationscreated'by the oscillating circuit, with the result the oscillations arefrequency modulated according to the voltage ap plied to the grid ofreactance tube VI. 7

The plate circuit of oscillator tube V2 is resistance coupled toacontrol grid circuit of amplifier tube V3 through a capacitor 39. Theplate circuit of the amplifier tube V3 is'powered from terminal B400through primary winding 40 of 'a coupling transformer T2. Primarywinding 40 and secondary winding 4| of the coupling transformer T2 arenormally tuned to resonance at the frequency fl by capacitors I04 and I;respectively, and by adjusting variable iron'cores. Secondary winding 4|of transformer T2 has-its outside terminals connected'to control grids4'2 and 43 of tubes V4 and V5, respectivelyfiof the power amplificationstage, 'and'itsmid terminal is connected to the negative terminal N32 ofthe power source through a biasing unit 44 so that each control grid 42and43 is provided witha preselected bias voltage. The plate circuits oftubes V4 and V5 include primary winding 45 of an output transformer T3in a push-pull arrangement. A first preselected portion of secondarywindin 46 of the output transformer T3 is connected through a backcontact of the relay 50 to a sending loop circuit the lead wires I38 andof which loop circuit are connected tothe pairs of wheels 4'! and 48 ofthe caboose. Such sending loop circuit is tuned to resonance at thefrequency fl through the use of a variable capac- 1?;1 5i connectedacross the lead Wires I38 and Relay 50 serves as a frequency change-overunit for the transmitting apparatus TA, the apparatus being conditionedto supply a ifllll'il'. telephone current of the channel frequency flwhen the relay is released and the transmitting apparatus beingconditioned to supply a different and a lower channel frequency which Ishall'call frequency f2 when the relay is picked up. When relay to isreleased the various elements of the transmitting apparatus are tuned inthe manner described hereinbefore and the apparatus is conditioned tosupply the channel frequency fl; but when the relay 50 is picked up in'a' manner to appear hereinafter, an -adjustable capacitor 52 isconnected through frontcontaot-53of relay-5M0 mitting apparatus TA it isapparent that when the the 'oscillating circuit and the" oscillationsare shifted to the carrier frequency f2. .:The primary winding 40andsecondary winding 4| of: coupling transformer T2 are shifted in theirtuning to the. channel frequency f2 by means of anxadjustable capacitorconnected across winding 40through front contact 55 of relay 50, and anadjustable capacitor 56 connected across winding 4 I through frontcontactv 51 of relay 50. Also, an adjustable capacitor 56 is connectedacross primary winde ing 45 of the output transformer T3 through frontcontact 59 of relay 50, an adjustable capacitor 60 is connected acrossthe sending loop cirr-x cuit through front contact 6| of the relay, anda second portion of the secondary winding. 46 of the output transformeris connected to the sending loop through front contact 62 of the relayto condition the circuits for the channel free-i quency fZ. t: Fromtheforegoing descriptionof the transfrequencychange-over relay 50 isreleased, trans mitting apparatus TA is conditioned to operate. on, thefirst channel frequency fl and when relay 5 0 is picked up thetransmitting apparatus is con-a ditioned to operate on the secondchannel fre: quency f2. It is also apparent that-voice frequencyvoltages appearing in the secondary winding l5 -of microphonetransformer TL cause through the reactance tube Vl, a correspondingfrequency modulation of the carrier created by the oscillating circuitfor tube V2, and such free quency modulated carrier current isamplified; to a predetermined energy levelandapplied to:.the sendingloop circuitof the caboose, such sending loop circuit including thetrack railsbetween the wheels 41 and 48 withtheresult that the com-1munication current is made to flow in a'track-t way transmitting circuitor channel including the rails and paralleling line wires in thewell-known manner. Since a smaller per cent frequency-swing is neededfor the same absolute frequency-swing at the higher channel frequency,and since less .oscillator capacity is used, the potential dividerl40 isinterposed-in the gridcircuit of tube VI when relay 50 .is released tocondition thetransmitter for the higher frequency fl and it isby-pass'ed when relay 50 is picked-up to condition the trans-, mitterfor the lower frequency f2." Inthis manher the same voice currentproduces the same ab solute frequency swing for both channel fre;

quencies. v r I shall now describe themicrophone circuit network withthe sensitivity adjustment ,pre emphasis, and modulatingindicationfeatures.

A microphone 63 of a hand set HS of the con-, trol unit CU has oneterminal connected, to ground electrode 64 and its other terminalconnected through wire 65 to a so-called L-pad66, the pad 66 beingconnected to ground through an impedance unit consisting of a capacitor-61 and a resistor 68 in multiple, and beingconnected through acircuitconnection including choke coil 69 to the terminal N32 of thecurrent source, Consequently the microphone network isf ener gi'zed fromthe 32 volt current source, the proper value of microphone current beingobtained by the correct value of the resistance of choke coil 69.Primary winding I4 of the microphone transformerTl is connected to aterminal of the pad 66 through a back contact 10 of the relay Hand toone terminal of coil 69. This L'-pad 66 is so constructed that it'presents a substantially con stantresistance to the "audiofrequencyfcurre nt fl w n n-the-m crophone circuit networkg" naeimpedances: of .the' pad :66 and capacitor -61 rot the impedanceunit:are chosen tobe of.susbtan-.-. tiallygthe'. same .order' attheshigher voicev fro-.- quency-of say 2400 cycles per second. Then fora lower voice frequency the impedance of capaci-- tor 61. becomesrelatively greater-than the resist-' ance componentof the impedance ofthe. microphone circuit and thecurrents flowing .are pro-- portionatelyreduced at the lower voice frequency. Thus at,600 cycles, the impedanceof capacitorfi'l would be about four times as great as theresistancelcomponents of the circuit and the current flowingwould beproportionately reduced. Re sistor 68 having about the same impedance ascapacitor vElfat 600.cycles, is shunted around capacitor Bl hand thesensitivity is maintained relatively constant at the reduced level forthe low voice-frequencies. Since pad 66 is chosen to have a constantinput impedance, changes of ad:- justmentiwill not change thepre-emphasis characteristic of the microphone circuit network.-Thus-.voice frequency voltages created in the microphone network areapplied to the controlgridof the reactance-tube VI at a preselectedamplitude such that an operator speaking very loud into the microphonewill not over swing the oscillations of the oscillating circuit for tubeV2.

The --modulation indicating feature includes tubes V6 and-V'l and anindication-lamp 11 located in the control unit CU. The tube V6 receives.power from the microphone circuit net work, a connection extending fromthe high voltageside of the secondary winding l through wire .'|'l andgrid leak unit 12' to control grid 13 of tube V6, cathode M of tube V5being -connectedto groundelectrode 20. The plate 75 of tube. V6 receivespower from terminal B400 through'front contact'24 of directional relay25, wire 26, resistors 21 and 28, wire 18 and resistor 19; The platecircuit of tube VB is'resistance coupled to the control grid 88) of tubeV! through capacitor 8i and the plate 82 of tube V1 receives power fromthe power source through abranch connection from wire l8, -resistor 83being interposed in the connection. Lamp 7! is preferably a glowdischarge tube, such as a neon tube, and it has one terminal groundedand its other terminal connected to the plate 82 of tube V! through wirel3 and a blocking capacitor 84. It follows that voice frequency voltagesappearing in the input-circuit of the'reactance tube V! are also appliedto tubes V6 and V1 and a corresponding amplified voltage is applied tothe lamp 11. The parts are proportioned so that a voice volt age-of apredetermined magnitude sufiicient to satisfactorily modulate thecarrier generatedby the oscillator tube V2 causes the lamp 11. to flash.Voltages below such predeterminedmagnitude will leave the lamp 17 dark.Thus, the sp eal ier by observing lamp ll can tell whenhe isspeak-. ingatthe correct loudness. It is tobepointed out that the .microphonecircuit network is ad: justecl at pad. Bliso thatthe background noiseofusual magnitude will notcreate voltages suflicient to properly modulatethe carrier frequency, but that voice frequencies above the energylevel-of the backgroundnoise causes proper operation'of the'transmittingapparatus and such magnitude of voice frequencies is required, to flashthe am flt.

A calling voltage is-applied to the input of the reactance tube VI formodulating thecarrier, by the calling means,.th'e calling voltagebeingof afrequency preselected to be of a diiferent tone iqr ucha pgl- Th tubV6 no ma ly sedtq amplify theindication' energy is switched to serve asarr/oscillator. for-. ;the. calling. means. When calling relay l9:isenergized in a. manner to later appear,.-the..=circuit for. primarywinding [4 of transformen-Tlis; opened at back .contact 10 sov thatthesecondary winding l5 of the transformer may have maximuminductanceand minimum powerv factor. An oscillating circuit network is formed bythe .t.op.; terminal of winding l5 being connected throughwire H andgrid leak unit 72 to,.,the.controlagrid .13 of tube. V6, cathode Itbeingv connected to an intermediate terminal of winding l5 .throughfrontcontact 88 of relay l9, platel5 :of .tubeVB being connected to anotherintermediate; terminal of winding l5 through blocking...capacitor 81;and front. contact I06 of relay .l9,;.and acapacitor 86 being connectedbetween the gridandcplate leads through front contact 85 of relay. l9 toform an oscillator tank circuit. Also, anadditional capacitor isconnected in multiple with capacitor 86 through back contact 9t ofthefrequency change-over relay 56. That :is, capacitors 86, and90 areconnected in multiple in. the tankbircuit .when the channel selectorrelay 50 isreleased andcapacitor 90 is removed from the tank .circuitwhen the relay 5!] is pickedup. It isv to be seen from this descrip tionthatwhen calling. relay I9 is picked up andthefrequencychange-overor-channel selector relay 50 is released, thetubeV6 functions as an oscillator to apply-oscillations of a preselectedtone frequency to the reactance tube VI and the carrier is frequencymodulated according to this tone frequency to provide a calling currentwhich is suppliedtothe .trackway transmitting circuit through thesending loop circuit; When relay l9 isipickedup and the relay 50 pickedup, the tube V6 is caused to serve as. an oscillator to supply a tonefrequency for modulating the second channel frequency .f2,:the secondtone frequency being different from that-supplied for the first channel.It is, to be..-noted that during such calling conditions, the .voltageappearing at the plate of tube V1 would be sufficiently high to excitethe indication; lamp 11, causing a constant illumination thereof.-However,- under such conditions, illumination of the. lamp is notdetrimental.

.Theemergencycalling means for alternating switching tube V6 to serve asan oscillator to provide the .callingtone for the first channel fl andtherrto provide the calling tone for the second channel f2 and toalternately repeat such operation will bemore-fullyexplained when theoperation of the apparatus is described.

The. receiving apparatus comprises two complete receivers designatedreceiver Fl and receiver.F2; respectively,-receiver- Fl being used forreception of .current of the channel frequency II- and receiversFz beingused to receive current of the second channel frequency f2, Thesereceivers-are alike except for'the tuning and each may beof-any one. ofseveral well-known arrangements; Each of the. receiverspreferablyincludes as essentialelements a high frequency amplifier, aconverter,.an intermediate frequency amplifier, a limiter, andadiscriminator. Each of these essential. elements, of the receiver isshown in block-form for. the sake .of simplicity because thespecifiostructure of each of these elements forms noupart. of my.invention and they may be of any one ,ofisevera-liwellsknownarrangements.

Two pick-yup coils:.92.:and.93. are mounted on the caboosefor inductiverelation with the trackwaytransmittingcircuit to pickup frequency 7modulated carriericurrentiapplied to such trackway circuit at a remotestation. -These twopickup coils 92 and 93 are connected to the inputside of the high frequency'amplifiers of the receivers Fl and F2,respectively.

The output of each discriminator of the two receivers is connected to acontrol grid of one section of a duo-triode tube V8, as willbe readilyunderstood by an inspection of Fig. 2. The plate circuits of the twosections of tube V8 are pow ered from the terminal B400 of the currentsource through proper resistors aswill'bealso'readily understood by aninspection of the drawing. The two plate circuits are coupled inmultiple through capacitors 98 and Illl' to a control grid 94 .of a loudspeaker amplifier tube V9, such connections of the plate circuits beingdescribed more fully shortly. Cathode 95 of tube'V9 is connected toground through a biasing unit 96, and the plate circuit of tube V9includes a winding of a transformer T4 to a secondary winding of whichtransformer a loud-speaker LS is connected.

When the hand set HS ofthe control unit CU is placed on the hookfswitchSl to close contact 97 and a triple-pole.double-throw switch S2 isthrown to the left, that is, to theposition illustrated in thedrawing','j;the couplingconnection from the plate circuit'of the"right-hand section of tube VB as viewed in the drawing'iscompletedthrough capacitor 98 contact blade 99 of switch S2, contact 91 of switchS'l, a'pre s'elected portion of a volume controlresistor I90, andcontrolgrid 94 of tube V9. Also, the coizplingponhection for left-hand sectiontr mps; V8... can ,betraced through capacitorIULcontact [blade I02 ofswitch S2 and volume control resistor.v I09 tocontrol grid 95 of tubeV9. When the switch" S2, is thrown to the right the connection of theleft-hand section of tube V8 to tube V9 is, then through contact blade99 of switch s2 and'thecontact 91 of the hook switch SI, andjtheconnection of the righthand section of tube V9 to tube V9is' through thecontact blade I02 of switch S2. Consequently when calling current ispicked up by either pickup 001192 or 93, such calling Icurrent isamplified and demodulated and the respective tone frequency current isapplied to .the loudspeaker, the tone sounded by the loud-speakerdepending upon the channel frequency. When the switch S2 is thrown tothe. left and the hand set'HS is removed from the hook/switchvtheleft-hand section of tube V8 remains connected to the tube V9 tosound a calling: current sent on the'channel frequency f2 but theoutputof the receiver Fl is disconnected from the tube V9 and isconnected to the earphone lll'l of the hand set,this connection beingcompleted'through the .contact I03 of the hook switch and a volumecontrol resistance let. Similarly, when the switch S2 is thrown to theright and the hand set, is removed from the hook switch the receiver Flremains connected to the loud speaker to sound'a callingcurrent sentover the frequency channel f-I .but'the output of receiver F2 isdisconnectedfromtheloud-speaker and the earphone of the hand set isconnected to the output of this receiver F2, the connection nowincluding the contact I93 of the'hook switch and the volume controlresistor I ll8.j The volume control resistor I99 is preferably providedwith stop i539 so that the sensitivity of the loud-speaker cannot bereduced below a desired limit.

The switch S2 also serves to determine the frequency channel of thetransmitting-apparatus.

When switch S2 'is thrown to'the'left a circuit is prepared for terminalN32 through contact blade I 10 I I l-, wire I ll, front contact I I8 andtransfer contact II5 of a continuity transfer type of contact of relay15, wire H6 and winding of frequency change-overrelay 50 to ground, andrelay 59 is normally deenergized to condition the transmittingforchannel fl. The relay 59 can be picked up and the'transmitterconditioned for channel )2 by the energizing of relay 16 when switch S2is thrown to the left. With switch S2 thrown to the right a circuit isformed from terminal N32 through'blade Ill, wire lI3, back contact H4and transfer contact I I5 of relay 16, wire I I5 and winding of relay 5Dto ground, and relay 5!] is normally picked up to-condition thetransmitter apparatus for channel f2, but relay 50 can be released andthe transmitter conditioned for channel fl by th picking up of relay it.

Also, when the frequency control switch S2 is thrown to the left toestablish channel fl, current flows from terminal N32 through blade IIIand lamp III! to ground and lamp III] is illuminated to indicate the useof channel fl. Similarly, with switch S2 thrown to the right, currentflows through lamp 2 and that lamp is illuminated to indicate the use ofchannel 2.

It follows that switch S2 serves as a frequency channel control device,the'left and right-hand positions of switch S2 selecting channels fl andf2; respectively. Such selection can be reversed, however, by relay I6.

I will next point out the circuits which reduce the sensitivity of thereceiver of the channel in use during the time of transmission at thesame station. Assuming that communication is being carried on throughchannel fl, a shunt circuit is formed across the" output side of thehigh fre- 'quency amplifier of receiver Fl, such shunt circuit beingtraced from one output terminal of the high frequency amplifier throughresistor H9, wire I20, back'contact I2l of relay 50 and front contactI22 of relay 25 to ground, the other output terminal of the highfrequency amplifier being also grounded. The-resistor H9 is proportionedso that during the sending period of the trans- Initter TA, the energypicked up by the coil 92 and'applied to the receiver Fl is shuntedsufficiently for the energy heard in the earphones tobe at aboutthesa'me level as that during the transmission from a remote station. Ina similar manner if communication is being carried on through channelf2, a shunt circuit is completed across the output side of the highfrequency amplifier of the receiver F2 during the sending period of thetransmitter; this shunt circuit extending from one output terminal ofthe associated high frequency amplifier through resistor 123; wire I24,front contact I25 of relay 50, front contact I22 of relay'25 and toground, the other output terminal of the respective high frequencyamplifier being grounded, It is clear, therefore, that'these shuntcircuits cause a reduction in the sensitivity of the receiver duringtransmission and each receiver will provide a satisfactory tell-talesound in the earphones of the hand set, such sound serving to indicatethe operativeness of the transmitting apparatus' and of the receivingapparatus then in use.

Referring to Fig. 3, there is disclosed means for coupling thetransmitting apparatus TA and the receiving apparatus RA of a waysidestation WS t'o'th'e transmitting channel. The transmitting apparatus TAandthe receiving apparatus RA are shown in Fig.v 3- in block form, "eachof these apparatuses being similar to the corresponding ppafhtus ofFigs. 1 and 2. A line wire Ll extends along the railway in eit-her orbothdirections from station WS and thisline wire may be an existing wireincluded in some present circuit or-it may be a wire placed on a poleline to serve as a part of the transmitting circuit. 7

' Secondary winding 46 of output transformer T3 of apparatus TA isconnected between line wire LI and ground through "contacts of thefrequency change-over relay 50. Substantially the full winding isincluded-in this connection when relay 56 is picked up to close frontcontact 62 and a preselected portion ofwinding 46 is included in theconnection when relay 50 is released closing back contact 49. Thus alarger voltage is applied to the transmitting circuit at the lowerchannel frequency f2. I

Since noise level is higher and- Government regulations permit a givenstrength of-energy at a greater distance from the line wire carrying thecurrent for the lower frequency, more turns of the A output Winding canbe used at the lower frequency. It is not necessary ordinarily to tunethis output circuit at a wayside station since the line wire presentsan'impedance with a relatively large resistive component. "Tuning can,of course, be used if desired.

The receivers ;FI and F2 are coupled to the transmitting circuit throughpick up coils 92" and 93 which are disposedin inductive relation to linewires L I.

Fig. 4'discloses a'second form of coupling the apparatus of'waysidestation WS to the trackway transmitting'circuit, Line'wires L2 and-L3extend along the railwayin either or both'directions from station WS andserve as elements of the transmitting circuit in the usual manner. Theseline wires L2 and L3'may be used in some other existing circuit. Twocapacitors I45 and H are connected inseries-across wires L2 and L3,'thefull winding 46 of output transformer T3 is connected betweenthe'junction terminal of capacitors J and I46 and ground through frontcontact 62 of frequency change -over relay 50, and a preselected portionof winding 46 is included in this connectionthrough back contact 49 ofrelay 5%. Thus the voltage applied to the transmitting apparatus TA ofthe transmitting circuit is of a value preselected according to thechannel frequencyused.

In Fig. 4 theinput terminals of receivers Fl and F2 are connectedbetween the junction terminal of capacitors I45 and I46 and ground. Itis clear that in Fig; 4 the wayside apparatuses are capacity coupled tothe transmitting circuit. It-is apparent-that-inductive coupling can beused in Fig: 4 either by inductive coilswound in'inductive relationtowires-LZ and L3'or another wire extending some distance-parallel towires L2 and L3. 1 A g In; describing the-operation of the apparatus, Ishall first consider Figs. 1 and- 2 and shall assume that the apparatusoccupies its normal position, that is, the position illustrated in thedrawings. At the start it is to be observed that the filaments-of thevarious tubes are all heated through suitable filament circuitsnotshown. Under this normal condition calling current may be picked upby coil92 due to some remote station sending out a calling current ofthe channel frequency fl. -Theenergy thus picked up is supplied to thereceiver Fl and after amplification and demodulation, the tone frequencycurrent is -applied to tube V8 and thence to tube V9- and to theloud-speaker whichsounds the calling tone to-inform' the operator thatcommunication is desired on the-channel frequency fl. -Similarly, ifenergy is picked up by the coil 93 due to a 'remote stationsending acalling currentof the channel frequencyf2 the pickedup energy is appliedto the receiver F2 and after amplification and demodulation :the tonecurrent is applied through tubes V8 andVS to the loud-speaker andthe-operator is-in'formed that communication is desired on channel f2;the operator distinguishing between the channlsby the different tones ofthe calling currents.

Assuming first that thecalling tone is for channel fl, the operatorwould set switch-S2 to the left if it is not already in that positionand would remove the handset HS from the hook to connect the hand set tothe output of the receiver Fl leaving the receiver F2 connected to theloudspeaker. The operator after removing the hand set from thehook'switch presses the press-totalk switch 5 on' the: hand setand'speaks an agreed salutation into the microphone 53. The closing ofthe press-to-talk switch 5 completes the connection for current to flowfrom battery terminal B32 to ground electrode 64 switch 5, wire E25 andWinding of directional relay 25 to battery terminal'N32; and thedirectional relay 25 'is picked up. The'picking up of relay 25 to closefront contact 24 applies plate voltage to the tubes of the transmittingapparatus, and the closingof front contact I22 of'relay 25 applies theshunt circuit across the receiver Fl, so that the transmitting apparatusexcited and the receiver Fl is'reduced insensitivity. With the tubes 'ofthe transmitter energized voice frequencies created by speaking into themicrophone 63' are applied to tube Vl with the result a frejquency'modulated carrier telephone current is applied-to the loop circuit andthence to the trackway transmitting circuit for transmission to remotestations. Such energy is also picked up by pick-up coil 92 and appliedto respective receiver'Fl' and the voice frequencies are reproduced at areduced energy level in the respective earphone 101 of the associatedhand set to check the operation of the apparatus. From this pointontwowaycbhvzrsation can be carried on between'the operator of thecaboose and the remote station by the operator properly operating thepress-to-talk switch 5.

It is clear that during sucha conversation through the communicationchannel fl, calling current can be received on the channel f2 and suchcalling tone 'soundedby the loud-speaker, such calling serving as abreak in.

Assuming next "that the calling current picked up is that 'for thechannel f2,' the operator to answer such call would first throw theswitch S2 to" the right and then remove'the'hand set HS from the hook.The throwing of the switch S2 completes the"circuit for the frequencychange-over relay 50 andthat relay picks up and conditions the"transmitting apparatus for operation' on-the "channel frequency f2. Theremoval of the handset 'from'thehook connects it to the output of thereceiver F2- leaving the receiver Fl connected to the loud-speaker forsounding any call that may be thereafter received on that channel. Fromthis point on the caboose operator can answer the call and carry on aconversation with a remote station through the channel f2 insubstantially thesame manner as explained in connection with thecommunication on the channel fl.

In connection with communication on either channeL-thespeaking at properloudness by the 13 operator will be indicated by the flashing of lamp TIin the manner explained hereinbefore.

If a conversation is being carried on through one channel and a call isreceived through the other channel, such call can be immediatelyanswered by the reversing of the switch S2. Also, the channel in usewill be indicated through the lamps III) and II2 of the controlunit Inthe event the operator on the caboose desires to initiate communication,he first sends a calling current corresponding to the channel throughwhich he wishes to communicata-selection of the channel being effectedbythe proper position of the switch S2. The operator would then depressa push button KI of the control unit to close contacts I2! and I28. Theclosing. of contact I21 of push button KI completes the circuit forenergizing relay 25 and that relay on picking up applies power to thetubes of the transmitting apparatus. The closing of contact I28 of thepush botton KI completes a circuit for current to flow from batteryterminal B32 through ground electrode I29, winding of relay I9, wire I30and contact I28 to battery terminal N32, and relay I9 is energized. Thepicking up of relay I9 switches tube V6 to serve as an oscillator andoscillations of thecalling frequency for the channel selected areapplied to the reactance tube VI to modulate the carrier and. acorresponding calling current is applied to the trackway circuit throughthe caboose loopcircuit. Subsequent to the proper answer back of such acalling current the operator would remove the hand set of the hookswitch and carry on a conversation in the manner previously explained.

In the event the caboose operator wishes to send an emergency callingcurrent, that is, a calling current alternately on each of .the twochannel frequencies, the operator depresses: a push button K2 Of thecontrol unit closing contacts i3I, I32 and I33. The closingof contactI3I completes the circuit for relay I9 and relay I9 on picking upswitches the tube V6 to serve as an oscillator. The closing of contactI33 of the push button K2 completes the circuitfor relay 25 and thatrelay on picking up applies power to the transmitting tubes. The closingof contact I32 of the push buttonKZ completes a circuit for relay 16,the circuit for relay 16 extending from positive terminal B32 through"ground electrode I34, back contact I35 of relay I6,winding of thatrelay, wire I36 and contact I32 to terminal N32. A capacitor I3! isconnected across the winding of relay Iii to cause this relay to beslowacting. Since relay IE is controlled throughits own back contact I35,this relay will alternately be energized and deenergized. The circuitfor changeover relay 53 is controlled through the contacts H4, H5 and H8of the relay I6 and thus with relay I3 alternately energized anddeenergized, the relay 5!! in turn is alternately picked up andreleased, and relay 50 when released conditions the transmittingapparatus to operate on channel frequency f I and when picked upconditions the transmitting apparatus to. operate on the channel f2. Itfollows, therefore, that as'long as the push button K2 is helddepressed, the'relay 16 causes the transmitting apparatus to bealternately conditioned for sending a calling current first on thefrequency channel fl and then on the'frequency channel f2. Suchemergency callingi'condition would be useful when it is desired tocallall trains with some of the trains carrying'on a communication throughchannel fl and'other' trains carrying on a communicationthrough'channelifil.

- Communication between an operator at. the wayside station of eitherFig. 3 or. Fig. 4 and a train would be carried on in substantially. thesame manner as just explained in connection with the station in cabooseCO.

Apparatusv such as here disclosed has the advantages that trains cancarry on a conversation on the different channels without interferencebetween different trains. A call can be received on a train on any oneof the channels and a call can be received on a train on the channel notin use to serve as a break in. Also, any station can call all the trainsirrespective of what channel they may be at the time carrying oncommunication through the emergency calling condition which alternatelysends pulses of calling current on the two channel frequencies.Furthermore, the usual background noise created at locations on a trainis suppressed and preemphasis is provided by adjustment of themicrophone circuit. Proper speaking during a conversation is indicatedto the operator. Checking of the integrity of the transmitting apparatusand of the receiving apparatus is provided and the use of frequencymodulation assures that noise created by static conditions is avoided.

Although I have herein shown and described but one form of railway traincommunication systems embodying my invention, it is understood thatvarious changes and modifications may be made therein within the scopeof the appended claims without departing from the spirit and scope of myinvention .iHaving thus described my invention, what I claim is:

1. In a railway train communication system for communication between thetrains of a division of the railway through a common transmitting mediumand by use of currents of different carrier frequencies, a plurality ofstations at least one for each train, each said station provided withcommunication equipment and which equipments are substantially alike forall stations; each said equipment including transmitting apparatus, re'ceiving apparatus, a frequency selector means and a telephone set; saidtransmitting apparatus having elements electrically coupled to saidtransmitting medium and including means capable of being differentlyconditioned to supply carrier telephone" current'of different carrierfrequencies, said receiving apparatus including an individual receiverfor each of said different carrier frequencies, each said receiverincluding an element electrically coupled to said transmitting mediumand each having means operable to demodulate carrier telephone'currentof the respective carrier frequency, each said receiver normally activefor 'each station to be ready to'receive on any one of said carrierfrequencies, and said selector means including circuit controllersoperable to different positions and circuit-s connected to thetransmitting and receiving apparatuses to preselect the condition of thetransmitting apparatus and to effectively connect said telephone set tothe receiver for the carrier frequency corresponding to the selectedcondition of the transmitting apparatus; whereby each station is enabledto communi'cate with any one of the other stations on any one of saidplurality of carrier frequencies and a plurality'of noninterferingtwo-way communication can be carried on simultaneously between aplurality of different pairs of said station's.

In a railway train communication system for communication between thetrains of a division o'f t'he' railwaythrough a common transmittingmedium'arld" by use ofcalling and' telephone "currents of a plurality'oi different carrier frequen cie's, a plurality orstations at least onefor each train; each said-station provided with communication equipmentand all of which equipments are substantially identical; each saidequipment including transmitting apparatus, receiving apparatus; controlmeans -a loud-speaker"and" a telephone hand set; said transmittingapparatus having elements electricallycoupled to said transmittingmedium and including" means capable of being"difi'erentlyconditioned tosupply a carrier telephone current of a-first or a'second carrierfrequeh-cycr a calling current of either said carrier frequenciesmodulated by an individualtone frecru'ency;v said receiving apparatusincluding: an independent receiver for each of said carrier frequenciesweacli said receiver including a' pick-up element electricallycoupled" to said transmitting medium and each-having means which'isnormally active-fordemodulating the telephone and cal-ling currents ofthe respective carrier frequency; andsaid control means includingcontacts operable to dififerent circuit arrangements tomor-m-ally-connect said receivers in multiple to said loud-speaker at a givennormal arrangement or itsccontacts and toselectively condition thetransmitting apparatus to supply calling and telephonecurre'nts ofapre'selected one of the carrier frequencies 'and'connectth-e telephoneset to the receiver ofsuch selected carrier frequency andthe-loud=speaker-to -the receiver of the non selected carrier atdiiTerentgiven operating ar rangements of-its-contacts', whereby eachstation can be called by any one of the other stations through itsloud-speaker on either ofsaid carriers andcommunicate by telephonethrough its telephone'set with-the calling-station and at the same timebeincondition to'receive a call or message through its loud-speaker fromany one of the otherstations.

'3. 'In arailway train communication system for communication'betweenthetrains of a division of the railwaythrough a commontransmitting medium, a 'pluralityof stations at least one for eachtrain; a plurality of substantially like commu-nication equipments oneat each of'said-statiohs and each of' which equipments includes amultiple frequency channel transmitting apparatus; a, multiple frequencychannel receiving apparatus, a-telephone set and a channel selectormeans; said transmitting apparatus having elements-electrically coupledto said transmitting medium and including devices which are capableof-beingdifierently-conditioned to supply carrier telephone current ofany one of the channel irequencies; said-transmitting apparatus at eachstation being normally inactive, said' receiving apparatus-including anindependent receiver for each "of-said channel frequencies, each said'receiver'having an element electrically coup-led to saidtransmittingmedium and including devices which are operable to detect thetelepholiecurrent of therespective channel frequency, each said receiver at eachstation being normally active,- said selector means includingcontrollers operable todifferent positions anda circuit-network ha-vingconnectionsto the transmitting and receiving apparatuses to preselectthe condition of-saidtransmitting apparatus and to efiectively connectsaid telephone set to the transmitting apparatus and to the receiver ofthe channel frequency corresponding to the selected condition ofthetransmitting apparatus, and a push-to-talk means at each said'stationoperable to selectively actlVatethe transmitting apparatus and the receiver with which'the telephone set is connected, whereby a plurality"of two-way telephone communications canbe-carried on simultaneouslybetween different pairs or said trains without in terferen'ce betweenthe different conversations.

i. In a railway train communication system the combination comprising;an electron tube oscillatorincluding an oscillating circuit and anelectron tube provided with input and output electrodes, said tubeelectrodes connected to the oscillating circuit in such amanner as togenerate a carrier frequency current, a, reactance electron tubeprovided with output electrodes and a control electrode, said outputelectrodes connected to the oscillating circuit of'said oscillator tofrequencymodulate the carrier according to voice frequenciesapplied tothe control electrode of said reactancetube; a circuit network includinga microphone, aresistance pad and a transformer and connected'to saidcontrol electrode of the reactancetube to apply voice frequencies tosaid control electrode; 'saidbircuitnetwork proportioned to suppressbackground noise below a given level, and indication means including avoice frequency energy responsive device and connected to said circuitnetwork to indicate when the energy applied to said control electrode isabove said given level to indicatecor'rect loudness ofspeakinginto'sai'cl microphone for satisfactory transmission of thecorresponding frequency modulated carrier telephone current.

5. In combinationjrailway train communication receiving" apparatus-Torreception of the telephone and "calling currents of a plurality ofdifferent carrier fre uency channels, said receiving 'apparatuscomprising an independent receiverfor eachof's'aid channels,aloud-speaker, an earphonegeachsaid receiver having input and outputcircuits" and-including a demodulating device capable of demcidulatingthe telephone and the'calling currents'of therespective carrierfrequency channelg-and manually operable switching' means having afirst-position to connect the output circuits of said receivers inmultiple to said loud=speaker-tosouhdthe calling tone of the callingcurrentor the speech of the telephone current of any of said channels,and saidswitching"means having other positions to connect the outputcircuit of any selected one of said receivers to said earphone with theoutput circuits of the remaining receivers connected to the loudspeakeronly to permit telephone communication through the channel of theselected receiven'the calling tone and spe'ech of any of the otherchannels being sounded at the loud-speaker.

6-. -In railway traincommuhication apparatus for reception- 0fa'plurality' ofdifferent carrier telephone currents, the combinationcomprising, a plurality of difierent-receivers one for each of saiddifferent telephone *currents, each said reoeiver'having input andoutput circuits and including means capable of'demodulating therespective carrier telephone"current, pick-up elements one connected'tothe input circuit of each of said receivers, a loudespeaker, a telephonehandset having a hook switch, and manually operable switching meanstocooperate with said hook switch to normallyconnect in multiple theoutput circuits of-said receivers to said loudspeaker and toselectivelyeonnect the earphone of the hand set to the output circuit ofany one of said receivers andthe output circuits of the remainingreceivers'in multiple to'th'e loud speaker.7..*Incombination;transmitting apparatus ill-'- eluding amodulator-oscillator, a microphone and a calling tone generator andwhich modulatoroscillator and tone generator are capable of beingdifferently conditioned to supply carrier telephone current of any oneof a plurality of different carrier frequencies and a calling currentfor each of said carrier frequencies, each said calling current beingthe carrier modulated with a predetermined tone frequency, a firstmanually controlled means having circuits connected to the transmittingapparatus to govern the conditions of the transmitting apparatus topreselect the carrier telephone current to be supplied, a secondmanually controlled means having circuits connected to the transmittingapparatus to govern the conditions of the transmitting apparatus topreselect the calling current to be supplied, and a third manuallycontrolled means having circuits connected to the transmitting apparatusto govern the conditions of the transmitting apparatus to cause thecalling currents to be supplied in a cyclic manner.

8. In combination, transmitting apparatus including amodulator-oscillator a microphone and a calling tone generator and whichdevices are capable of being differently conditioned to supply carriertelephone current of either a first or a second carrier frequency and acalling current of either of said carrier frequencies, each said callingcurrent being the carrier modulated by a predetermined tone frequency, afirst control relay operable to a first and a second position to governthe conditions of the transmitting apparatus to preselect the carrierfrequency to be supplied, a second control relay operable to a first anda second position to govern the conditions of the transmitting apparatusto preselect the supplying of telephone current or'of calling current,and a third control relay capable of code operation to govern theconditions of the transmitting apparatus to supply the calling currentsalternately.

9. In combination, an electron oscillator tube having input electrodesand output electrodes which are connected to an oscillating circuit togenerate a carrier frequency current, an electron reactance tube havinga control electrode and output electrodes and which output electrodesare connected to said oscillating circuit to frequency modulate thecarrier according to the voltages applied to the control electrode ofthe reactance tube; a circuit network including a microphone, aresistance pad, and a'trans'former connected to said control electrodeto apply voice frequency voltages forfrequency modulating said carrier;said circuit network proportioned for only voice currents above apredetermined energy level to be effective for modulating the carrier tosuppress background noise, and indication means includin an amplifierand an indicatorconnected to said circuit network to indicate voicecurrents above said predetermined energy level.

10. In combination, an electron tube oscillator having input and outputelectrodes which are connected to an associated oscillating circuit togenerate oscillations of a predetermined carrier frequency, an electronreactance tube having a control electrode and output electrodes andwhich output electrodes are connected to said oscillating circuit tofrequency modulate the oscillations according to voltages applied to thecontrol elec-- trode of said reactance tube; a circuit network includinga microphone and an impedance unit connected to said control electrodeto apply voice frequency voltages for supplying in the output of saidoscillator a frequency modulated carrier telephone current, andindication means including an amplifier electron tube and an indicatorlamp connected to said circuit network to illuminate said lamp only whenthe voice current of the network is above a predetermined energy level.

11. In combination, an electron tube oscillator having an electron tubewhich is provided with input and output electrodes that are connectedtoan associated oscillating circuit to generate oscillations of apredetermined carrier frequency, an electron reactance tube having acontrol grid and output electrodes and which output electrodes areconnected to said oscillating circuit to frequency vary the oscillationsaccording to voltages app-lied to the control grid of the reactancetube; a circuit network including a, microphone, a resistance pad, animpedance unit and a transformer connected to said control grid to applyat times voice frequency voltages to said control grid for supplying inan output circuit of said oscillator tube a corresponding frequencymodulated carrier telephone current, and said resistance pad andimpedance unit proportioned to pro-emphasize the higher voicefrequencies.

12. In combination, transmitting apparatus including an electron tubeoscillator having an electron tube provided with input and outputelectrodes and an oscillating circuit, said oscillating circuitconnected to said tube electrodes in such a manner as to generatecarrier frequency current, said oscillator capable of being differentlyconditioned to supply carrier current of either a first or a secondfrequency, control means having connection to said transmittingapparatus to govern said conditions, an electron modulator tube having acontrol electrode and output electrodes, said output electrodes beingcoupled to said oscillator to frequency modulate said carrierfrequencies according to the voltage applied to the control electrode ofsaid modulator tube, a circuit network including a microphone connectedto said control electrode to apply voice frequency voltages thereto tofrequency modulate whichever carrier is being supplied, and a potentialdivider including resistance interposed in said circuit network andgoverned by said control means to control said voice frequency voltagesto effect substantially the same absolute frequency swing in themodulations of said carrier frequencies.

13. In a railway train communication system for communication between awayside station and trains operating over a given territory of saidrailway through a transmitting circuit which includes a line wireextending along the trackway, the combination comprising, a waysidetransmitting apparatus including means' capable of being differentlyconditioned to supply carrier telephone current of a first or a secondcarrier frequency, said transmitting apparatus coupled to saidtransmitting circuit by being connected to said line wire and ground,and control means interposed in said connection to apply to thetransmitting circuit a voltage predetermined for each said carrierfrequency and which voltage is larger for the lower of the two carrierfrequencies.

14. In a railway train communication system for communication between awayside station and trains operating over a given territory of said ingmeans capable of being differently conditioned to supply carriertelephone current of a apparatus including means operable to demodulatesuch carrier telephone currents, two capacitors connected in seriesacross a pair of said line wires, a first connection to connect inputterminals of said receiving apparatus between a junction terminal ofsaid capacitors and ground, a second connection to connect outputterminals of said transmitting apparatus between said junction terminaland, ground, and said second connection including control means to applyto the transmitting circuit a voltage predetermined'for each conditionof the transmitting apparatus and which voltage is larger for the lowerof the two carrier frequencies.

15. In a railway train communication system which provides equipment onall or nearly all of thetrains of a division for telephone communicationon either a first or a second frequency channel and for each of whichchannels a carrier telephone current and a calling current are provided,each said equipment including transmitting apparatus and' receivingapparatus, each said transmitting apparatus havin means capable of beingconditioned to supply the'calling current for each said frequencychannel with each said calling current having an individualcharacteristic, each said receiving apparatus including two independentreceivers one for each said frequency channel, each said receiver havingmeans for detecting the calling current and the carrier telephonecurrent of the same channel, the receivers of each of said trainsnormally active to detect the calling current of the respectivefrequency channel and each receiver capable of being conditioned toreceive the telephone current of the respective frequency channel,control means for each such train, and each control means havingcircuits connected to the transmitjting apparatus and including acontroller operable to' at times'condition' the transmittin 'apparatusof the same train to supply the calling currents of said first andsecond frequency channels alternately to call all trains when some ofthe trains are telephoning on one frequency channel and others on theother frequency channel. 16. In combination, transmitting apparatusincluding means capable of being conditionedto supply telephone currentof any one of a plurality of different frequency channels and a callingcurrent for each said channel and also an emergency calling circuit,each said calling current having an individual characteristic, a firstcontrol means including a controller and circuits connected to thetransmitting apparatus and operable to different positions to controlsaid trans mitting apparatus to preselect the frequency channel, asecond control means including a controller and circuits connected tothe transmitting apparatus and operable to different positions tocontrol said transmitting apparatus to supply the calling current forthe channel preselected by said first control means, and a third controlmeans including a controller and circuits connected to the transmittingapparatus and operable to control the transmitting apparatus to supplyan emergency calling current of a distinctive characteristicirrespective of the position of said first control means.

17. In a railway train telephone system for two-way communicationbetween different train carried stations each of which stations isequipped with a telephone transmitter and a receiver using a carrierfrequency telephone current, the combination comprising, push-to-talkreceiver of the station for reception and to deenergize the transmitter,generating means at a station capableof supplying oscillationsof apreselected tone frequency but normally inactive, circuit connections toconnect said generating means to the transmitter of the same station tomodulate the carrier by said oscillations, a circuit interrupter devicenormally deenergized, means including contacts of said interrupterdevice connected with said generating means to cause the generatingmeans to recurrently supply said oscillations to create a distinctivesignaling current of the modulated carrier, and control means havingcircuits and a circuit controlling switch operable to at times energizesaid transmitter, to render said generating means active and to energizesaid circuit interrupter device to sound at the receiver of each of theassociated stations a distinctive signal.

18. In a railway train communication system for telephone communicationbetween the trains and selected wayside offices of a railway by use of acommon transmitting medium and by the use of calling and telephonecurrents of a plurality of different carrier frequency channels, acommunication station on each of the trains and at each of the ofiices,each said station provided with communication equipment all of which aresubstantially alike to enable any one of the stations to communicatewith any other one of the stations; each said equipment includingtransmitting apparatus, receiving apparatus, selector means, a controlcircuit means, a loud-speaker and a telephone set; each saidtransmitting apparatus including a transmitter having means capable ofbeing difierently conditioned for supplying calling and telephonecurrents of any one of the plurality of different carrier frequencies,each said transmitter having an element coupled to the transmittingmedium but normally inactive, each said receiving apparatus including anindividual receiver for each of the different carrier frequencies, eachsaid receiver having -means operable to demodulate the calling andtelephone currents of the respective carrier frequency, each saidreceiver having an element coupled to the transmitting medium andnormally active, the receivers of each station having their outputsconnected in multiple to the loudspeaker of the same .station to enableeach station to receive a call from any one of the other stations on anyone of the carrier frequencies, each said selector means including acontroller operable to different positions and circuits connected tosaid transmitter and receivers to select by its position and conditionof the transmitter of the same station and to connect the telephone setto the receiver of the station for the carrier frequency correspondingto the carrier frequency of the selected condition of the respectivetransmitter, the loud- =speaker being disconnected from the selectedredifferent carrier frequency channels to enable 'each vehicle totelephone to any other vehicle by use of a common transmitting medium,communication equipment on each said vehicle and all of which equipmentsare substantially alike; each said equipment including transmittingapparatus, receiving apparatus, a telephone set and selector circuitmeans; each said transmitting apparatus including means capable of beingdifierently conditioned to supply carrier telephone current of any oneof the plurality of difierent carrier frequency channels, each saidtransmitting apparatus having elements disposed for communicationrelationship With the transmitting medium but normally inactive, eachsaid receiving apparatus including an individual receiver for each ofsaid different carrier frequency channels, each said receiver includingmeans capable of demodulating carrier telephone current of therespective carrier channel and having elements disposed forcommunication relationship with the transmitting medium in a normallyactive condition, each said selector circuit means including circuitsconnected to said transmitter and receiving apparatuses and operable todifferent conditions to select by its condition the condition of thetransmitting apparatus of the same vehicle and to 22 effectively couplethe telephone set to the transmitting apparatus and to the receiver ofthe carrier channel corresponding to that selected for the transmittingapparatus.

PAUL N. BOSSART.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,821,758 Konn Sept, 1, 19312,064,639 Whitelock et a1 Dec. 15, 1936 2,064,641 Bossart Dec. 15, 19362,064,958 Taylor et al Dec. 22, 1936 2,090,088 Whitelock Aug. 17, 19372,124,450 Shaver July 19, 1938 2,143,563 Levy et a1 Jan. 10, 19392,176,868 Boswan Oct. 24, 1939 2,272,106 Ash Feb. 3, 1942 2,419,593Robinson Apr. 29, 1947 Certificate of Correction Patent No. 2,484,680October 11, 1949 PAUL N. BOSSART It is hereby certified that errorappears in the printed specification of the above numbered patentrequiring correction as follows:

Column 19, line 52, for the word circuit read current;

and that the said Letters Patent should be read with this correctiontherein that the same may conform to the record of the case in thePatent Office. Signed and sealed this 31st day of January, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

